Here's a stab in the dark about this.

So we know you are eating VLC. Robb Wolf and others like Kurt Harris talk about the fact that over time VLC can cause one to become temporarily insulin resistant. This is an adaptation to eating VLC and not a disease state.

So, when one is insulin resistant, insulin is not clearing glucose from the blood fast enough and you become hyperglycemic. This causes increased urine output as a result. Among other things). This is one reason why when folks talk about reintroducing carbs after vlc or lc, they are coached to titrate them up slowly, in order to get the body's metabolic machinery going in that direction again (whether that direction is the right way is another topic altogether).

So, my guess is that you peed out some water due to the high blood glucose you had after eating starch while on a vlc plan. Overnight fat loss in pounds does not happen - I think.

Someone with a biochem background may likely tear this idea apart.

A familiar pattern for women eating paleo for fat loss: tried eating VLC to jump start fat loss, saw no fat loss or even some gain, switched to moderate carb and usually started counting calories, got desired fat loss.

Weighing a couple pounds less the day after eating some starch isn't a reliable measure of 'weight loss' I have to say. I would start logging your intake. See what you're eating now in terms of macros/calories, and try some calculated variations. See what works for you. People truly are different.

Some people experience intense hunger on VLC diets which leads to high consumption of fat/calories. I think this is the main reason VLC isn't a good tool for weight loss for everyone (it does work for many - a majority seem to get suppressed appetite). Many people also feel better generally with moderate carbs in their diet.

I seem to be losing weight for the first time in three years since adding a small evening potato or sweet potato to my diet. I eat a Dr. K-esque low carb, high protein breakfast - usually 3 eggs, 1/4 lb of grass-fed ground beef and lacto-fermented salsa - and fast through lunch (which is no sweat thanks to the big breakfast). Dinner is usually steak or ground beef with a small potato (diced and broiled with a tablespoon of coconut oil = pure heaven). We also do a lot of slow-cooked beef stew and soups made from bone broth, beef or chicken, veg and some kind of potato.

According to Cronometer, I'm eating about 50% fat, 30% protein and 20% carb. There may be multiple factors at work here, but I find that the addition of the potato helps me to stay inside a lower calorie framework - ~1,100 calories, since my life is fairly sedentary at the moment.

I experience it all the time, and my wife. It happens that my weight is constant on VLC but if I eat ice cream or something, it starts going down. I don't know how to explain that except that for some reason sugar is not absorbed because of enzyme downregulation or something... if its absorbed, it will be used to recover glycogen ASAP which comes with x3 water weight and by all logic you would get weight. If I overeat carbs, like I eat 3 ice creams instead 1, that is indeed what happens

As always, organism is very good at adaptation. Thats why I like the concept of cheat day. Adaptation means you are more efficient, so you get more energy from the food you eat. By switching to another type of fuel, you revert efficiency.

My only problem with eating bunch of carbs after prolonged VLC is the idea that it will all be absorbed and that pancreas will not give enough insulin so lots of sugar will hag out in the blood forming AGEs, like with diabetics. I don't know if that happens, since I don't have sugar meter, but I believe it does (judging from the fact that VLCs often fail OGTT if they do not introduce carbs few days before). That wold mean that cheat day is actually harmful. If somebody has more info on this, I would appreciate any input.

Some people think that this phenomenon comes from the carb cycling itself, not the higher carb days in isolation. Unfortunately for me, I've never experienced it.

I often notice this if I do it one a week. It also happens if I eat alot of wild salmon in a given day.